Fuel cell stack assembly

ABSTRACT

An improved proton exchange membrane fuel cell assembly and fuel cell stack assembly are provided for the economical and efficient production of electricity. The present invention comprises improved flow fields and reactant supply systems, which provide improved and more efficient mass transport of the reactants in the fuel cell and the fuel cell stack assembly. The improved flow fields comprise three-dimensional open-cell foamed metals that are preferably plated with gold. The improved reactant supply system comprises an improved distribution frame to house fuel cells wherein the reactants are directly connected to the improved flow fields.

RELATED REFERENCES

This application is a divisional of application Ser. No. 09/669,344,filed Sep. 26, 2000 now U.S. Pat. No. 6,531,238.

BACKGROUND OF THE INVENTION

The present invention relates in general to the field of proton exchangemembrane (“PEM”) fuel cell systems, and more particularly, to animproved PEM fuel cell system having improved discrete fuel cell moduleswith improved mass transport for ternary reaction optimization and amethod for manufacturing same.

A fuel cell is an electrochemical device that converts fuel and oxidantinto electricity and a reaction by-product through an electrolyticreaction that strips hydrogen molecules of their electrons and protons.Ultimately, the stripped electrons are collected into some form ofusable electric current, by resistance or by some other suitable means.The protons react with oxygen to form water as a reaction by-product.

Natural gas is the primary fuel used as the source of hydrogen for afuel cell. If natural gas is used, however, it must be reformed prior toentering the fuel cell. Pure hydrogen may also be used if storedcorrectly. The products of the electrochemical exchange in the fuel cellare DC electricity, liquid water, and heat. The overall PEM fuel cellreaction produces electrical energy equal to the sum of the separatehalf-cell reactions occurring in the fuel cell, less its internal andparasitic losses. Parasitic losses are those losses of energy that areattributable to any energy required to facilitate the ternary reactionsin the fuel cell.

Although fuel cells have been used in a few applications, engineeringsolutions to successfully adapt fuel cell technology for use in electricutility systems have been elusive. Fuel cells would be desirable in thisapplication because they convert fuel directly to electricity at muchhigher efficiencies than internal combustion engines, thereby extractingmore power from the same amount of fuel. This need has not beensatisfied, however, because of the prohibitive expense associated withsuch fuel cell systems. For a fuel cell to be useful in utilityapplications, the life of the fuel cell stack must be a minimum of fiveyears and operations must be reliable and maintenance-free. Heretoforeknown fuel cell assemblies have not shown sufficient reliability andhave disadvantageous maintenance issues. Despite the expense,reliability, and maintenance problems associated with heretofore knownfuel cell systems, because of their environmental friendliness andoperating efficiency, there remains a clear and present need foreconomical and efficient fuel cell technology for use in residential andlight-commercial applications.

Fuel cells are usually classified according to the type of electrolyteused in the cell. There are four primary classes of fuel cells: (1)proton exchange membrane (“PEM”) fuel cells, (2) phosphoric acid fuelcells, and (3) molten carbonate fuel cells. Another more recentlydeveloped type of fuel cell is a solid oxide fuel cell. PEM fuel cells,such as those in the present invention, are low temperature low pressuresystems, and are, therefore, well-suited for residential andlight-commercial applications. PEM fuel cells are also advantageous inthese applications because there is no corrosive liquid in the fuel celland, consequently, there are minimal corrosion problems.

Characteristically, a single PEM fuel cell consists of three majorcomponents—an anode gas dispersion field (“anode”); a membrane electrodeassembly (“MEA”); and a cathode gas and liquid dispersion field(“cathode”). As shown in FIG. 1, the anode typically comprises an anodegas dispersion layer 502 and an anode gas flow field 504; the cathodetypically comprises a cathode gas and liquid dispersion layer 506 and acathode gas and liquid flow field 508. In a single cell, the anode andthe cathode are electrically coupled to provide a path for conductingelectrons between the electrodes through an external load. MEA 500facilitates the flow of electrons and protons produced in the anode, andsubstantially isolates the fuel stream on the anode side of the membranefrom the oxidant stream on the cathode side of the membrane. Theultimate purpose of these base components, namely the anode, thecathode, and MEA 500, is to maintain proper ternary phase distributionin the fuel cell. Ternary phase distribution as used herein refers tothe three simultaneous reactants in the fuel cell, namely hydrogen gas,water vapor and air. Heretofore known PEM fuel cells, however, have notbeen able to efficiently maintain proper ternary phase distribution.Catalytic active layers 501 and 503 are located between the anode, thecathode and the electrolyte. The catalytic active layers 501 and 503induce the desired electrochemical reactions in the fuel cell.Specifically, the catalytic active layer 501, the anode catalytic activelayer, rejects the electrons produced in the anode in the form ofelectric current. The oxidant from the air that moves through thecathode is reduced at the catalytic active layer 503, referred to as thecathode catalytic active layer, so that it can oxidate the protonsflowing from anode catalytic active layer 501 to form water as thereaction by-product. The protons produced by the anode are transportedby the anode catalytic active layer 501 to the cathode through theelectrolyte polymeric membrane.

The anode gas flow field and cathode gas and liquid flow field aretypically comprised of pressed, polished carbon sheets machined withserpentine grooves or channels to provide a means of access for the fueland oxidant streams to the anode and cathode catalytic active layers.The costs of manufacturing these plates and the associated materialscosts are very expensive and have placed constraints on the use of fuelcells in residential and light-commercial applications. Further, the useof these planar serpentine arrangements to facilitate the flow of thefuel and oxidant through the anode and cathode has presented additionaloperational drawbacks in that they unduly limit mass transport throughthe electrodes, and therefore, limit the maximum power achievable by thefuel cell.

One of the most problematic drawbacks of the planar serpentinearrangement in the anode and cathode relates to efficiency. Inconventional electrodes, the reactants move through the serpentinepattern of the electrodes and are activated at the respective catalyticlayers located at the interface of the electrode and the electrolyte.The actual chemical reaction that occurs at the anode catalyst layer is:H₂Ξ2H⁺+2e⁻. The chemical reaction at the cathode catalyst layer is:2H⁺+2e⁻+½O₂ΞH₂O. The overall reaction is: H₂+½O₂ΞH₂O. The anodedisburses the anode gas onto the surface of the active catalyst layercomprised of a platinum catalyst electrolyte, and the cathode disbursesthe cathode gas onto the surface of the catalytic active layer of theelectrolyte. However, when utilizing a conventional serpentineconstruction, the anode gas and the cathode gas are not uniformlydisbursed onto the electrolyte. Nonuniform distribution of the anode andcathode gas at the membrane surface results in an imbalance in the watercontent of the electrolyte. This results in a significant decrease inefficiency in the fuel cell.

The second most problematic drawback associated with serpentinearrangements in the electrodes relates to the ternary reactions thattake place in the fuel cell itself. Serpentine arrangements provide nopressure differential within the electrodes. This prohibits thenecessary ternary reactions from taking place simultaneously. This isparticularly problematic in the cathode as both a liquid and a gas aretransported simultaneously through the electrode's serpentine pattern.

Another shortcoming of the conventional serpentine arrangement in theanode in particular is that the hydrogen molecules resist the inevitableflow changes in the serpentine channels, causing a build-up of moleculardensity in the turns in the serpentine pattern, resulting in temperatureincreases at the reversal points. These hot spots in the serpentinearrangement unduly and prematurely degrade the catalytic active layerand supporting membrane.

In the typical PEM fuel cell assembly, a PEM fuel cell is housed withina frame that supplies the necessary fuel and oxidant to the flow fieldsof the fuel cell. These conventional frames typically comprise manifoldsand channels that facilitate the flow of the reactants. However, usuallythe channels are not an integral part of the manifolds, which results ina pressure differential along the successive channels. FIG. 2 is anillustration of a conventional frame for the communication of thereactants to a fuel cell. This pressure differential causes thereactants, especially the fuel, to be fed into the flow fields unevenly,which results in distortions in the flow fields causing hot spots. Thisalso results in nonuniform disbursement of the reactants onto thecatalytic active layers. Ultimately, this conventional method ofsupplying the necessary fuel and oxidant to a fuel cell results in avery inefficient process.

As a single PEM fuel cell only produces about 0.30 to 0.90 volts D.C.under a load, the key to developing useful PEM fuel cell technology isbeing able to scale-up current density in individual PEM cell assembliesto produce sufficient current for larger applications withoutsacrificing fuel cell efficiency. Commonly, fuel cell assemblies areelectrically connected in nodes that are then electrically connected inseries to form “fuel cell stacks” by stacking individual fuel cellnodes. Two or more nodes can be connected together, generally in series,but sometimes in parallel, to efficiently increase the overall poweroutput.

Conventional PEM fuel stacks often flood the cathode due to excess waterin the cathode gas flow field. Flooding occurs when water is not removedefficiently from the system. Flooding is particularly problematicbecause it impairs the ability of the reactants to adequately diffuse tothe catalytic active layers. This significantly increases the internalresistance of the cathode which ultimately limits the cell voltagepotential. Another problem is dehydration of the polymeric membraneswhen the water supply is inadequate. Insufficient supply of water candry out the anode side of the PEM membrane electrolyte, causing asignificant rise in stack resistance and reduced membrane durability.

Further, conventional PEM fuel cells and stacks of such fuel cellassemblies are compressed under a large load in order to ensure goodelectrical conductivity between cell components and to maintain theintegrity of compression seals that keep various fluid streams separate.A fuel cell stack is usually held together with extreme compressiveforce, generally in excess of 40,000 psi, using compression assemblies,such as tie rods and end plates. If tie rods are used, the tie rodsgenerally extend through holes formed in the peripheral edge portion ofthe stack end plates and have associated nuts or other fastening meansassembling the tie rods to the stack assembly to urge the end plates ofthe fuel stack assembly toward each other. Typically, the tie rods areexternal, i.e., they do not extend through the fuel cellelectrochemically active components. This amount of pressure that mustbe used to ensure good electrochemical interactions presents manyoperational difficulties. For example, if the voltage of a single fuelcell assembly in a stack declines significantly or fails, the entirestack must be taken out of service, disassembled, and repaired,resulting in significant repair costs and down-time. Second, inadequatecompressive force can compromise the seals associated with the manifoldsand flow fields in the central regions of the interior distributionplates, and also compromise the electrical contact required across thesurfaces of the plates and MEAs to provide the serial electricalconnection among the fuel cells that make up the stack. Third, theextreme compressive force used unduly abrades the surfaces of the fuelcell modules within the stack, resulting in wear of components in thefuel cell assemblies such as the catalyst layers of the electrolyte,thereby leading to increased losses in fuel cell stack and fuel cellassembly efficiency.

SUMMARY OF THE INVENTION

Herein provided is a fuel cell assembly and fuel cell stack assembly.One embodiment of a fuel cell of the present invention comprises (a) adistribution frame having: (i) an anode side, a cathode side and acentral cavity suitable for housing a fuel cell assembly; (ii) at least2 fuel inlet apertures, the fuel inlet apertures extending completelythrough the distribution frame and each fuel inlet aperture beinglocated 180° from the other, and each fuel inlet aperture having aninterior side; (iii) an air inlet aperture, the air inlet apertureextending completely through the distribution frame and the air inletaperture being located 90° from each fuel inlet aperture and 180° froman air and water outlet aperture, the air and water outlet apertureextending completely through the distribution frame, the air inletaperture and the air and water outlet aperture each further having aninterior side; (iv) a plurality of fuel supply channels, the fuel supplychannels located on the anode side of the distribution frame andextending from the interior side of each fuel inlet aperture to thecentral cavity and being integral to each fuel inlet aperture; aplurality of air supply channels, the air supply channels located on thecathode side of the distribution frame and the air supply channelsextending from the interior side of the air inlet aperture to thecentral cavity and being integral to the air inlet aperture; and (vi) aplurality of air and water outlet channels, the air and water outletchannels located on the cathode side of the distribution frame, the airand water outlet channels extending from the interior side of the airand water outlet aperture to the central cavity, and being integral tothe air and water outlet aperture; and (b) a fuel cell assembly having:(i) an MEA having two catalytic active layers, the MEA further having ananode side and a cathode side, the MEA having an electrolyte; (ii) a gasdiffusion layer, the gas diffusion layer having a top face and a bottomface, the bottom face of the gas diffusion layer juxtaposed to the anodeside of the electrolyte; (iii) a gas and liquid diffusion layer, the gasand liquid diffusion layer having a top face and a bottom face, the topface of the gas and liquid diffusion layer juxtaposed to the cathodeside of the electrolyte; (iv) an anode gas flow field comprising athree-dimensional open-cell foamed structure suitable for gas diffusion,the anode gas flow field juxtaposed to the top face of the gas diffusionlayer; and (v) a cathode gas and liquid flow field comprising athree-dimensional open-cell foamed structure suitable for gas and liquiddiffusion, the cathode gas and liquid flow field juxtaposed to thebottom face of the gas and liquid diffusion layer; the fuel cellassembly being located within and integral to the central cavity of thedistribution frame, and being located such that the gas and liquid flowfield is contiguous to the air supply channels and the air and wateroutlet channels so as to form an edge-on connection with the air supplychannels and the air and water outlet channels, and located such thatthe gas flow field is contiguous to the fuel supply channels so as toform an edge-on connection with the fuel supply channels.

One embodiment of fuel cell stack of the p.i. comprises: (a) a first endplate and a second end plate, the second end plate being aligned withthe first end plate; (b) at least one fuel cell, the fuel cell beinginterposed between the first end plate and the second end plate and thefuel cell further comprising: (i) a distribution frame having: (A) ananode side, a cathode side and a central cavity suitable for housing anMEA; (B) at least 2 fuel inlet apertures, the fuel inlet aperturesextending completely through the distribution frame and each fuel inletaperture being located 180° from the other, and each fuel inlet aperturehaving an interior side; (C) an air inlet aperture, the air inletaperture extending completely through the distribution frame and the airinlet aperture being located 90° from each fuel inlet aperture and 180°from an air and water outlet aperture, the air and water outlet apertureextending completely through the distribution frame, the air inletaperture and the air and water outlet aperture each further having aninterior side; (D) a plurality of fuel supply channels, the fuel supplychannels located on the anode side of the distribution frame andextending from the interior side of each fuel inlet aperture to thecentral cavity and being integral to each fuel inlet aperture; (E) aplurality of air supply channels, the air supply channels located on thecathode side of the distribution frame and the air supply channelsextending from the interior side of the air inlet aperture to thecentral cavity and being integral to the air inlet aperture; and (F) aplurality of air and water outlet channels, the air and water outletchannels located on the cathode side of the distribution frame, the airand water outlet channels extending from the interior side of the airand water outlet aperture to the central cavity, and being integral tothe air and water outlet aperture; and (ii) a fuel cell assembly having:(A) an MEA, the MEA having two catalytic active layers, the MEA furtherhaving an anode side and a cathode side; (B) a gas diffusion layer, thegas diffusion layer having a top face and a bottom face, the bottom faceof the gas diffusion layer juxtaposed to the anode side of the MEA; (C)a gas and liquid diffusion layer, the gas and liquid diffusion layerhaving a top face and a bottom face, the top face of the gas and liquiddiffusion layer juxtaposed to the cathode side of the MEA; (D) an anodegas flow field comprising a three-dimensional open-cell foamed structuresuitable for gas diffusion, the anode gas flow field juxtaposed to thetop face of the gas diffusion layer; and (E) a cathode gas and liquidflow field comprising a three-dimensional open-cell foamed structuresuitable for gas and liquid diffusion, the cathode gas and liquid flowfield juxtaposed to the bottom face of the gas and liquid diffusionlayer; the fuel cell assembly being located within and integral to thecentral cavity of the distribution frame, and being located such thatthe gas and liquid flow field is contiguous to the air supply channelsand the air and water outlet channels so as to form an edge-onconnection with the air supply channels and the air and water outletchannels, and located such that the gas flow field is contiguous to thefuel supply channels so as to form an edge-on connection with the fuelsupply channels; and (c) a compression assembly.

Other advantages of the present invention will be apparent to thoseordinarily skilled in the art in view of the following specificationclaims and drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present embodiments and advantagesthereof may be acquired by referring to the following description takenin conjunction with the accompanying drawings, in which like numbersindicate like features, and wherein:

FIG. 1 is a schematic of a typical PEM fuel cell assembly.

FIG. 2 is an illustration of a conventional frame for housing andsupplying reactants to a fuel cell assembly.

FIG. 3 is a depiction of a distribution frame of the present inventionhousing a fuel cell assembly.

FIG. 4 is an exploded view of the distribution frame and a fuel cellassembly of the present invention.

FIG. 5 is a cross-sectional view of an internal foil assembly of thepresent invention.

FIG. 6 is an electron micrograph of a three-dimensional open-cell foamedcathode gas and liquid flow field with microchannels.

FIG. 6A is an electron micrograph of the three-dimensional open-cellfoamed cathode gas and liquid flow field with microchannels of thepresent invention magnified 10 times.

FIG. 6B is an electron micrograph of the three-dimensional open-cellfoamed cathode gas and liquid flow field with microchannels of thepresent invention magnified 20 times.

FIG. 7 is an electron micrograph of the connections between athree-dimensional open-cell foamed gas flow field and an internal foilin an internal foil assembly of the present invention.

FIG. 8 is an electron micrograph of the connections between thethree-dimensional open-cell foamed gas flow field magnified 150 times.

FIG. 9 is an electron micrograph of two individual connections betweenthe three-dimensional open-cell foamed gas flow field and the internalfoil of an internal foil assembly of one embodiment of the presentinvention.

FIG. 10 is an electron micrograph of a conventional internal foilassembly formed using conventional techniques.

FIG. 11 is an illustration of the fuel side of a distribution frame fora fuel cell assembly of the present invention.

FIG. 12 is an illustration of the air side of a distribution frame for afuel cell assembly of the present invention.

FIG. 13 is an illustration of a fuel cell stack assembly of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3 depicts one embodiment of an individual fuel cell assembly of thepresent invention. As shown in FIG. 3, fuel cell 11 is housed withindistribution frame 10. Distribution frame 10 not only houses fuel cell11, but also facilitates transportation of the fuel and the oxidant tothe fuel cell necessary for the electrochemical exchange in the fuelcell. This individual fuel cell assembly can be combined with other fuelcell assemblies to form a fuel cell node, and ultimately a stackassembly, to provide higher voltages and current for power generation.Of note in FIG. 3 are fuel inlet 22, fuel inlet 24, air inlet 12 and airand water outlet 14. The fuel inlets 22 and 24, air inlet 12, and airand water outlet 14 are apertures in the distribution frame extendingcompletely through the distribution frame, and run perpendicular, or at90° angles, from one another in the distribution frame to facilitate theefficient flow of the fuel and oxidant to and through the anode gas andliquid flow field and cathode gas flow field, respectively.

FIG. 4 more particularly illustrates the component parts of the fuelcell assembly of one embodiment of the present invention depicted inFIG. 3, specifically distribution frame 10, primary internal foilassembly 64, fuel cell 11 and secondary internal foil assembly 30.Primary internal foil assembly 64 consists of primary anode gas flowfield 52, primary internal foil 54 and primary cathode gas and liquidflow field 56. Primary internal foil 54 serves as a boundary layerbetween primary anode gas flow field 52 and primary cathode gas andliquid flow field 56 to keep air from flowing into the anode gas flowfield from the cathode and water from flowing from the cathode gas andliquid flow field to the anode gas flow field. MEA 58 is composed of anelectrolyte, primary cathode catalytic active layer 60, and secondaryanode catalytic active layer 62. Any known MEAs may be used in thepresent invention. Conventional fluorocarbon based polymeric membranesare particularly suitable for the present invention-includingperfluorinated polymer membranes such as NAFION membranes. Primarycathode catalytic active layer 60 is bonded to primary cathode gas andliquid flow field 56 when the fuel cell is assembled. Secondary internalfoil 31 also serves as a boundary layer between the anode and cathodeelectrodes of the internal foil assembly as does primary internal foil54. Secondary anode catalytic active layer 62 is bonded to secondaryanode gas flow field 29 when the fuel cell assembly is assembled. FIG. 4illustrates the assembled fuel cell placed in distribution frame 10wherein secondary cathode gas flow field 28 is in view. Secondaryinternal foil 31 is also illustrated in FIG. 3.

When the fuel cell assembly of the present invention is assembled as inthe embodiments depicted in FIGS. 3 and 4, the procession of layers is:primary anode gas flow field 52, primary internal foil 54, primarycathode gas flow field 56, MEA 58, secondary anode gas flow field 29,secondary internal foil 31, and secondary cathode gas flow field 28.This defines the elements of one fuel cell of the present inventionterminated by internal foil assemblies. Primary cathode catalyst layer60 and secondary anode catalyst layer 62 of the MEA shown in FIG. 4 maybe comprised of platinum or a platinum/ruthenium catalyst. If platinumis used, it is typically combined with fibrous material, includingsuitable nonwovens, or suitable cotton muslin sheets or pieces offabric. Primary cathode gas flow field 56 and secondary anode gas flowfield 29 are bonded to primary cathode catalytic active layer 60 andsecondary anode catalytic active layer 62, respectively, throughmechanical bonding means such as compression or adhesion. However, thereis no need for excessive compressive force in the present invention tocreate the electrochemical connections between the catalytic activelayers and the gas flow fields. Compression may be provided by any knownmeans, such as a tie-rod assembly. In general, the compressive force ona fuel cell stack should be less than 100 psi.

FIG. 5 is a cross-section of an internal foil assembly of the presentinvention. Internal foil assembly 64 is comprised of three parts: anodegas flow field 66, internal foil 68, and cathode gas and liquid flowfield 70. The cross section of the anode gas flow field 66 may bepreferably approximately half the size of cathode gas and liquid flowfield 70 to accommodate the ratios of reactants necessary for theelectrochemical exchange in the fuel cell. Both anode gas flow field 66and cathode gas and liquid flow field 70 may be composed of athree-dimensional open-cell foamed structure suitable for gas diffusionthat, preferably, may be plated with gold. In another embodiment of thepresent invention, cathode gas flow field 70 may be corrugated to createmicrochannels. FIG. 6 illustrates a corrugated cathode gas and liquidflow field of the present invention. These microchannels facilitate theremoval of free water and excessive heat from the fuel cell assembly.When the fuel cell is placed in the distribution frame, thesemicrochannels in the cathode gas and liquid flow field 70 run parallelto the air inlet and air and water outlet, and perpendicular to the fuelinlets. The vertical distance between the peak of a corrugation and thetrough next to it, herein referred to as the pitch, should be at least ⅔of the horizontal distance between a peak of one corrugation to the peakof the next corrugation, herein referred to as the run. Whereas, asshown in FIG. 5, anode gas flow field 66 is directly bonded to internalfoil 68; in an alternative embodiment cathode gas and liquid flow field70 is only bonded to the internal foil at the peaks of the corrugations.As shown in FIG. 6, the cathode gas and liquid flow field is thereforeintermittently bonded to the internal foil at the peaks of themicrochannels. This structure effectively manages the ternary reactionsnecessary for fuel cell operability by adequately removing the water andfacilitating the movement of hydrogen and air. FIGS. 6A and 6B depictmagnified views of the microchannels shown in FIG. 6.

Suitable construction materials for the three-dimensional open-cellfoamed gas flow fields and gas and liquid flow fields are conducive toflow distribution and possess good electrical conductivity properties.These may include: plastics, carbon filament, stainless steel and itsderivatives, epitaxial substrates, nickel and its alloys, gold and itsalloys, and copper and its alloys. Iridium may also be used if it hassufficient electrochemical properties. In one embodiment of the presentinvention, the anode gas flow field and the cathode gas and liquid flowfields are made from open-cell foamed nickel. The open-cell foamednickel flow fields are produced by electroplating nickel over aparticulate plastic so that the voids created by the tangentialintersections in the particulate plastic structure are filled withnickel. Although polystyrene may be used in this method of producing thefoamed flow field structure, other materials, such as other particulatethermoplastic resinous materials, would also be suitable in thisprocess. Another suitable material, for example, would be Isinglass. Ifnickel is used, the nickel may be enhanced with 2.0% by weight ofcobalt. The addition of cobalt enhances the mechanical strength of thenickel and reduces the drawing properties of the nickel. The addition ofcobalt also strengthens the lattice structure of the finished open-cellfoamed flow field. Once the nickel has cooled, the polystyrene plasticmay be blown out of the foam with hot carbon dioxide gas or air leavinga three-dimensional nickel open-cell foamed flow field structure havingsubstantially five-sided geometrically-shaped orifices. The nickelfoamed flow field is autocatalytically microplated with up to 15 micronsof gold, iridium, copper or silver. Preferably, the flow field ismicroplated, with between 0.5 to 2.0 microns of gold.

FIGS. 7 and 8 are electron micrographs of a three-dimensional open-cellfoamed flow field of the present invention wherein the substantiallyfive-sided orifices are visible and have been plated with gold. Theadvantage obtained from utilizing a three-dimensional open cell foamedflow field in the present invention is that it enhances mass transferwithin the flow fields. This is because the mass transfer rate issupplemented by the foamed flow field itself and its wicking ability,which allows the molecules to electromosaticaly move through the flowfield. Another advantage associated with the foamed flow fields of thepresent invention is that they also facilitate the deposit of thereactants uniformly along the surface of the catalytic active layers. Afurther distinct advantage of the foamed flow fields over conventionalserpentine arrangements is that the foamed flow fields enhance theternary reactions of the fuel cell. The gold plating further enhancesthe electromosatic movement of the molecules through the flow fields byproviding microridges, evident in FIGS. 7 and 8, on the surfaces of thefoamed structure's orifices. These microridges facilitate the flow ofthe fuel, oxidant, and water in the flow fields. The gold platingenhances mass transfer by increasing the surface area of the foam by asmuch as a factor of nine. Another advantage of gold plating the foamedflow field of the present invention is that the leaflet potential of thegold preserves the structure of the foamed flow fields by preventing theflow fields from undergoing electrolysis. This enhances the life of theflow fields and the fuel cell assembly itself, making the fuel cellassemblies of the present invention suitable for residential andlight-commercial uses.

As shown in FIG. 5, in internal foil assembly 64, anode gas flow field66 and cathode gas and liquid flow field 70 are attached to primaryinternal foil 68 through mechanical bonding, such as sintering, plating,pressing, rolling, drawing, or extruding. Another connections meanswould include laminating through electrochemical adhesives. Thisincreases the electrical conductivity through the internal foil assemblyby decreasing the air gap between the flow fields and the internal foil.Preferably, internal foil 68 is plated with gold as are the flow fieldsso as to create an undisturbed electrical connection between the flowfields and the internal foil. When a gold-plated nickel foam is used, analloy of copper and silver should be used to sinter the gold plated,nickel foam to internal foil assembly 64.

FIG. 9 is an electron micrograph of one embodiment of the internal foilassembly of one embodiment of the present invention illustrating theconnection as shown in FIG. 5 between anode gas flow field 66, cathodegas flow field 70, and internal foil 68, wherein all three elements havebeen gold plated. As can be particularly seen by the arrows in FIG. 9,the substantially five-sided orifices of the open-cell foamed gas flowfields are not deformed by the bonding process of the present invention.FIG. 10 comparatively illustrates the deformation the gas flow fieldsuffer if bonded to the internal foil using conventional techniques. Theelectrically consistent connection achieved in the present inventionbetween the flow fields and the internal foil provides for moreefficient mass transfer in the internal foil assembly of the presentinvention.

Shown in FIG. 11 is one embodiment of the anode side (as indicated byreference numeral 120) of distribution frame 10. Fuel inlet 12 and fuelinlet 14 provide the fuel to the fuel cell housed within the cavity ofdistribution frame 10 necessary for the electrochemical reaction.Specifically, the fuel is fed to the anode gas flow field through fuelsupply channels 18 and 16 that stretch from the interior sides orsurfaces of fuel inlet 12 and fuel inlet 14, respectively. Fuel supplychannels 18 and 16 are shaped such that the supply of the fuel to theanode is preferably maintained at a constant velocity, i.e., thechannels are of sufficient length, width and depth to provide fuel tothe anode at a constant velocity. The velocity of the fuel entering theanode gas flow field via fuel supply channels 18 and 16 may be less thanthe velocity of oxidant entering the cathode gas flow field via airsupply channels 25. The number of fuel supply channels in thedistribution frame stoichiometrically balances the number of air supplychannels so as to achieve a 2.0 to 1.0 to 2.8 to 1.0, preferably 2.0 to1.0 to 2.4 to 1.0, air to fuel ratio. Fuel supply channels 18 and 16also provide an edge-on connection between the fuel supply inlets andthe anode gas flow field of the fuel cell housed within the cavity ofthe distribution frame to allow for enhanced dispersion of the fuelthrough the anode gas flow field. Suitable materials of construction fordistribution frame 10 include nylon-6, 6, derivatives of nylon-6, 6,polyetheretherketone (“PEEK”), ABS styrene, a polyester film such asMYLAR mylar, textar, a polyamide such as KEVLAR kevlar or any othernonconductive thermoplastic resin. Preferably, distribution frame 10 isformed from nylon-6, 6, and, if used in a stack assembly, the end platesof the fuel cell stack assembly are preferably formed from PEEK.Nylon-6, 6 is a particularly suitable material for distribution frame 10because it dissipates electrical energy quickly so that it will notaccumulate in the fuel cell assembly. It also has good compressionproperties. Distribution frame 10 is preferably substantially circular.

Shown in FIG. 12 is the cathode side (as indicated by reference numeral140) of distribution frame 10. Air is a necessary reactant for theelectrochemical exchange, and may be fed to fuel cell 11 via air inlet24 in combination with air supply channels 26. Air supply channels 26stretch from the interior surface or side of air inlet 24 to fuel cell11, and are of such sufficient size and shape that they enable air to befed to the cathode gas flow field at a constant velocity, i.e., they areof sufficient height, width and depth. The number of fuel supplychannels 18 and 16 will most often exceed the number of air supplychannels 26 to maintain a stoichiometric balance of the reactants. Freewater is formed continuously in the cathode gas and liquid flow field asa by-product of the electrochemical reaction. As described, theopen-cell foamed of the cathode gas and liquid flow field facilitatesthe removal of this free water from the cathode gas and liquid flowfield efficiently. In an alternative embodiment of the present whereinthe cathode gas flow field is corrugated, the microchannels in thecathode gas flow field enhance free water removal from the system. Airand water outlet 22 and air and water outlet channels 25 facilitate theflow of this free water from fuel cell 11 to allow for optimal watermanagement in the fuel cell, and to avoid flooding and the resultantloss in power. In a stack assembly, this free water may be transportedfor use in other parts of the fuel cell unit, unit here meaning thebalance of plant assembly. Air and water outlet 22 and air and wateroutlet channels 25 also facilitate dissipation of the heat generated bythe electrochemical reactions.

FIG. 13 is a cross-section of a fuel cell stack assembly shown generallyat 200 that encompasses a plurality of fuel cell assemblies. Two or moreindividual fuel cell assemblies can be combined to form a node. Two ormore nodes can be combined to form a fuel cell stack assembly.Typically, these individual fuel cells will be interposed between endplates, which are preferably substantially circular. Stacks can beplaced in series to increase voltage. Stacks can be arranged in parallelto increase amperes. In one embodiment of the present invention, 1 endplate is used for every 6 fuel cell assemblies frames to providedesirable torsional properties to the fuel cell stack assembly.

Although the present disclosure has been described in detail, it shouldbe understood that various changes, substitutions, and alterations canbe made hereto without departing from the spirit and the scope of theinvention as defined by the appended claims.

1. A fuel cell comprising: (a) a distribution frame having: (i) an anodeside, a cathode side and a central cavity suitable for housing a fuelcell assembly; (ii) at least 2 fuel inlet apertures, the fuel inletapertures extending completely through the distribution frame and eachfuel inlet aperture being located 180° from the other, and each fuelinlet aperture having an interior side; (iii) an air inlet aperture, theair inlet aperture extending completely through the distribution frameand the air inlet aperture being located 90° from each fuel inletaperture and 180° from an air and water outlet aperture, the air andwater outlet aperture extending completely through the distributionframe, the air inlet aperture and the air and water outlet aperture eachfurther having an interior side; (iv) a plurality of fuel supplychannels, the fuel supply channels located on the anode side of thedistribution frame and extending from the interior side of each fuelinlet aperture to the central cavity and being integral to each fuelinlet aperture; (v) a plurality of air supply channels, the air supplychannels located on the cathode side of the distribution frame and theair supply channels extending from the interior side of the air inletaperture to the central cavity and being integral to the air inletaperture; and (vi) a plurality of air and water outlet channels, the airand water outlet channels located on the cathode side of thedistribution frame, the air and water outlet channels extending from theinterior side of the air and water outlet aperture to the centralcavity, and being integral to the air and water outlet aperture; and (b)a fuel cell assembly having: (i) an MEA having two catalytic activelayers, the MEA further having an anode side and a cathode side, the MEAhaving an electrolyte; (ii) a gas diffusion layer, the gas diffusionlayer having a top face and a bottom face, the bottom face of the gasdiffusion layer juxtaposed to the anode side of the electrolyte; (iii) agas and liquid diffusion layer, the gas and liquid diffusion layerhaving a top face and a bottom face, the top face of the gas and liquiddiffusion layer juxtaposed to the cathode side of the electrolyte; (iv)an anode gas flow field comprising a three-dimensional open-cell foamedstructure suitable for gas diffusion, the anode gas flow fieldjuxtaposed to the top face of the gas diffusion layer; and (v) a cathodegas and liquid flow field comprising a three-dimensional open-cellfoamed structure suitable for gas and liquid diffusion, the cathode gasand liquid flow field juxtaposed to the bottom face of the gas andliquid diffusion layer; the fuel cell assembly being located within andintegral to the central cavity of the distribution frame, and beinglocated such that the gas and liquid flow field is contiguous to the airsupply channels and the air and water outlet channels so as to form anedge-on connection with the air supply channels and the air and wateroutlet channels, and located such that the gas flow field is contiguousto the fuel supply channels so as to form an edge-on connection with thefuel supply channels.
 2. The fuel cell according to claim 1 wherein thecathode gas and liquid flow field has corrugations, the corrugationscreating microchannels, the corrugations further having a pitch and arun.
 3. The fuel cell according to claim 2 wherein the pitch of thecorrugations is greater than or equal to ⅔ of the run of thecorrugations.
 4. The fuel cell according to claim 1 wherein the anodegas flow field comprises nickel, alloys of nickel, copper, alloys ofcopper, gold or alloys of gold.
 5. The fuel cell according to claim 1wherein the cathode gas and liquid flow field comprises nickel, alloysof nickel, copper, alloys of copper, gold, and alloys of gold.
 6. Thefuel cell according to claim 1 wherein the anode gas flow field or thecathode gas and liquid flow field are plated with gold, platinum oriridium.
 7. The fuel cell according to claim 1 wherein the MEA furthercomprises a platinum or platinum/ruthenium catalyst.
 8. The fuel cellaccording to claim 1 wherein the electrolyte is a perfluorinated polymerelectrolyte.
 9. The fuel cell according to claim 1 wherein the gasdiffusion layer and the gas and liquid diffusion layer comprises acotton fibrous layer and a platinum or platinum/ruthenium catalyst. 10.The fuel cell according to claim 1 wherein the distribution frame issubstantially circular.
 11. The fuel cell according to claim 1 whereinthe distribution frame comprises nylon 6,6, derivatives of nylon 6,6,polyetheretherketone, ABS styrene, a polyester film, or a polyamide. 12.The fuel cell according to claim 1 wherein the number of fuel supplychannels exceeds the number of air supply channels.
 13. A fuel cellstack comprising: (a) a first end plate and a second end plate, thesecond end plate being aligned with the first end plate; (b) at leastone fuel cell, the fuel cell being interposed between the first endplate and the second end plate and the fuel cell further comprising: (i)a distribution frame having: (A) an anode side, a cathode side and acentral cavity suitable for housing an MEA; (B) at least 2 fuel inletapertures, the fuel inlet apertures extending completely through thedistribution frame and each fuel inlet aperture being located 180° fromthe other, and each fuel inlet aperture having an interior side; (C) anair inlet aperture, the air inlet aperture extending completely throughthe distribution frame and the air inlet aperture being located 90° fromeach fuel inlet aperture and 180° from an air and water outlet aperture,the air and water outlet aperture extending completely through thedistribution frame, the air inlet aperture and the air and water outletaperture each further having an interior side; (D) a plurality of fuelsupply channels, the fuel supply channels located on the anode side ofthe distribution frame and extending from the interior side of each fuelinlet aperture to the central cavity and being integral to each fuelinlet aperture; (E) a plurality of air supply channels, the air supplychannels located on the cathode side of the distribution frame and theair supply channels extending from the interior side of the air inletaperture to the central cavity and being integral to the air inletaperture; and (F) a plurality of air and water outlet channels, the airand water outlet channels located on the cathode side of thedistribution frame, the air and water outlet channels extending from theinterior side of the air and water outlet aperture to the centralcavity, and being integral to the air and water outlet aperture; (ii) afuel cell assembly having: (A) an MEA, the MEA having two catalyticactive layers, the MEA further having an anode side and a cathode side;(B) a gas diffusion layer, the gas diffusion layer having a top face anda bottom face, the bottom face of the gas diffusion layer juxtaposed tothe anode side of the MEA; (C) a gas and liquid diffusion layer, the gasand liquid diffusion layer having a top face and a bottom face, the topface of the gas and liquid diffusion layer juxtaposed to the cathodeside of the MEA; (D) an anode gas flow field comprising athree-dimensional open-cell foamed structure suitable for gas diffusion,the anode gas flow field juxtaposed to the top face of the gas diffusionlayer; and (E) a cathode gas and liquid flow field comprising athree-dimensional open-cell foamed structure suitable for gas and liquiddiffusion, the cathode gas and liquid flow field juxtaposed to thebottom face of the gas and liquid diffusion layer; the fuel cellassembly being located within and integral to the central cavity of thedistribution frame, and being located such that the gas and liquid flowfield is contiguous to the air supply channels and the air and wateroutlet channels so as to form an edge-on connection with the air supplychannels and the air and water outlet channels, and located such thatthe gas flow field is contiguous to the fuel supply channels so as toform an edge-on connection with the fuel supply channels; and (c) acompression assembly.
 14. The fuel cell stack according to claim 13wherein the first end plate and the second end plate are constructed ofpolyetheretherketone.
 15. The fuel cell stack according to claim 13wherein the first end plate and the second end plate are substantiallycircular.
 16. The fuel cell stack according to claim 13 wherein thefirst end plate and the second end plate further comprise apertures foruse in conjunction with the compression assembly.
 17. The fuel cellstack according to claim 13 wherein the compression assembly includes aplurality of tie rod assemblies.
 18. The fuel cell stack according toclaim 13 wherein the distribution frame of the fuel cell issubstantially circular.
 19. The fuel cell stack according to claim 13wherein the cathode gas and liquid flow field has corrugations.
 20. Thefuel cell stack according to claim 19 wherein the corrugations have apitch and a run, and wherein the pitch is greater than or equal to ⅔ ofthe run.
 21. The fuel cell stack according to claim 13 wherein the anodegas flow field comprises nickel, alloys of nickel, copper, alloys ofcopper, gold or alloys of gold.
 22. The fuel cell stack according toclaim 13 wherein the cathode gas and liquid flow field comprises nickel,alloys of nickel, copper, alloys of copper, gold, and alloys of gold.23. The fuel cell stack according to claim 13 wherein the anode gas flowfield or the cathode gas and liquid flow field are plated with gold,platinum or iridium.
 24. The fuel cell stack according to claim 13wherein the electrolyte further comprises a platinum or aplatinum/ruthenium catalyst.
 25. The fuel cell stack according to claim13 wherein the electrolyte is a perfluorinated polymer electrolyte. 26.The fuel cell stack according to claim 13 wherein the gas diffusionlayer and the gas and liquid diffusion layer comprise a fibrous layer.27. The fuel cell stack according to claim 13 wherein the distributionframe is substantially circular.
 28. The fuel cell stack according toclaim 13 wherein the distribution frame comprises nylon 6,6, derivativesof nylon 6,6, polyetheretherketone, ABS styrene, a polyester film, or apolyamide.
 29. The fuel cell stack according to claim 13 wherein thenumber of fuel supply channels stoichiometrically balances the number ofair supply channels so as to achieve an air to fuel mixture of between2.0 to 1.0 to 2.4 to 1.0.
 30. A method of inducing an electrochemicalreaction so as to generate electricity comprising: (a) providing a fuelcell stack comprising: (i) a first end plate and a second end plate, thesecond end plate being aligned with the first end plate; (ii) at leastone fuel cell, the fuel cell being interposed between the first endplate and the second end plate and the fuel cell further comprising: (A)a distribution frame having: (1) an anode side, a cathode side and acentral cavity suitable for housing an MEA; (2) at least 2 fuel inletapertures, the fuel inlet apertures extending completely through thedistribution frame and each fuel inlet aperture being located 180° fromthe other, and each fuel inlet aperture having an interior side; (3) anair inlet aperture, the air inlet aperture extending completely throughthe distribution frame and the air inlet aperture being located 90° fromeach fuel inlet aperture and 180° from an air and water outlet aperture,the air and water outlet aperture extending completely through thedistribution frame, the air inlet aperture and the air and water outletaperture each further having an interior side; (4) a plurality of fuelsupply channels, the fuel supply channels located on the anode side ofthe distribution frame and extending from the interior side of each fuelinlet aperture to the central cavity and being integral to each fuelinlet aperture; (5) a plurality of air supply channels, the air supplychannels located on the cathode side of the distribution frame and theair supply channels extending from the interior side of the air inletaperture to the central cavity and being integral to the air inletaperture; and (6) a plurality of air and water outlet channels, the airand water outlet channels located on the cathode side of thedistribution frame, the air and water outlet channels extending from theinterior side of the air and water outlet aperture to the centralcavity, and being integral to the air and water outlet aperture; and (B)a fuel cell assembly having: (1) an MEA, the MEA having two catalyticactive layers, the MEA further having an anode side and a cathode side;(2) a gas diffusion layer, the gas diffusion layer having a top face anda bottom face, the bottom face of the gas diffusion layer juxtaposed tothe anode side of the MEA; (3) a gas and liquid diffusion layer, the gasand liquid diffusion layer having a top face and a bottom face, the topface of the gas and liquid diffusion layer juxtaposed to the cathodeside of the MEA; (4) an anode gas flow field comprising athree-dimensional open-cell foamed structure suitable for gas diffusion,the anode gas flow field juxtaposed to the top face of the gas diffusionlayer; and (5) a cathode gas and liquid flow field comprising athree-dimensional open-cell foamed structure suitable for gas and liquiddiffusion, the cathode gas and liquid flow field juxtaposed to thebottom face of the gas and liquid diffusion layer; the fuel cellassembly being located within and integral to the central cavity of thedistribution frame, and being located such that the gas and liquid flowfield is contiguous to the air supply channels and the air and wateroutlet channels so as to form an edge-on connection with the air supplychannels and the air and water outlet channels, and located such thatthe gas flow field is contiguous to the fuel supply channels so as toform an edge-on connection with the fuel supply channels; and (iii) acompression assembly; (b) conveying hydrogen to the fuel cell stack; (c)conveying air to the fuel cell stack; and (d) generating electricity viaan electrochemical reaction using the fuel cell stack.